This invention relates generally to diagnostic imaging methods and apparatus, and more particularly, to methods and apparatus that provide detectors that are useful in computed tomography (CT).
Most multi-slice CT scanners are built with detectors composed of scintillator/photodiodes arrays. The photodiodes arrays are mainly based on front-illuminated technology. However, new designs based on back-illuminated photodiodes are being developed for CT machines to overcome the challenge of the higher number of runs and connections required. Current CT detectors generally use scintillation crystal/photodiode arrays, where the scintillation crystal absorbs x-rays and converts the absorbed energy into visible light. A photodiode is used to convert the light to an electric current. The electric current is read and the reading is proportional to the total energy absorbed. In these designs, the signal detected by the diode represents the integrated energy of the x-ray flux, during a short period of time, without any discrimination of energy.
Recently new ideas of CT detectors are being investigated for energy discrimination purposes using particularly direct conversion x-ray detector (or photoconductor) material such as CZT, CdTe, PbO, and etc., based photo-detectors. In this document, all direct conversion x-ray detectors are referred to as direct conversion material (CDM) detectors. These detectors are capable of photon counting and then measuring the energy of every photon. However, there is still a major challenge to overcome in order to achieve good CT performance and quality. Most of these detectors, working in photon counting modes are limited in their counting rate, either by pile-up effect, saturation, dynamic range, etc.
Besides, these detectors typically saturate at relatively low x-ray flux levels, which makes the detector feasible only in very low flux conditions. Therefor, described below is a detector which can be used in high x-ray flux environments. One way to overcome this limitation (limited count rate) is to find a method to provide energy information using integrating detectors such as in conventional CT systems. For this purpose, dual KVp systems can respond to the need because they do not suffer from count-rate limitations, as they typically used conventional detectors, operating in integrating mode. However, since the two data sets are acquired some distance apart in space or in time, this approach will be limited in its ability to resolve rapid changes in anatomy due to organ motion. When combined with a data acquisition system which is capable of resolving the energy of individual photon events, the system provides energy information which is not available in conventional CT. The advantage is that the energy information is provided simultaneously which enables the avoidance of motion related errors.
The proposed invention provides energy discrimination by interleaving data channels with different spectral responses. The combination of a) interleaving of channels having different spectral sensitivities and b) focal spot deflection will lead to a CT system with two or several images at different x-ray energies, or spectral windows. This patent describes the different ways of achieving detectors with different spectral responses.